This invention relates to low strength concrete compositions to be used as back fill grouts. These compositions are capable of solidifying into inexpensive, low strength materials for back filling excavations where it is desirable to avoid subsidence of the back filled materials subsequent to the back filling operation. They are pumpable with sufficient viscosity to remain free of settling out or separation of components during pumping, and are of low enough viscosity to take advantage of the void-filling capability of the grout.
As is known in the art, an admixture is a material other than hydraulic cement, water, fiber reinforcement or aggregates which is used as an ingredient of concrete or mortar and is added to the batch immediately before or during its mixing or use. Admixtures are used to modify the properties of concrete or grout in such a way as to make it more suitable for a particular purpose or for economy. Using an admixture should allow the employment of less expensive construction methods or designs or achieve new results and thereby offset the costs of the admixture. U.S. Pat. No. 4,961,790 discloses additional information regarding admixtures generally, and is hereby incorporated by reference.
The present invention concerns the use of an admixture for increasing the viscosity of a cementitious grout or blend containing a high proportion of aggregate and a very low proportion of cement which, without the admixture, would be of very limited use due to the settling of the aggregate from the mixture.
One material commonly used to fill cavities is referred to as CLSM, Controlled Low Strength Material. This material can be discharged from the chute of a ready mix truck directly into the cavity to be filled, whereupon the material will set into a low strength concrete useful for filling cavities resulting from excavation operations. When such a cavity is inaccessible by truck or where it is necessary for the material to flow or be pumped over some distance to its final destination, CLSM material presents difficulties and generally can not be used due to separation and settling out of the aggregate contained in such mixtures.